The present invention relates to electromagnetic compatibility (EMC) seals for use in joints within electronic assemblies and more particularly, relates to faceplates having an EMC seal between them in a rack and/or an EMC seal between a faceplate and a shelf.
Electronic equipment emits signals, known as electromagnetic interference (EMI), which can interfere with the electronic equipment itself or with other devices. As more electronic equipment is used, the potential for interference between the electronic equipment increases. Electromagnetic compatibility (EMC) is a measure of how well electronic equipment shares the electromagnetic environment without adverse effects from EMI. The goal of EMC is to construct electronic equipment with sufficiently low electromagnetic emissions and electromagnetic susceptibility. Electronic equipment can also be damaged by electrostatic discharge (ESD). As a result, electronic equipment must comply with stringent industry standards for EMC and ESD.
EMC and ESD standards must be met for a rack of printed wiring boards stacked side by side, for example, as used. in the telecommunications industry. Faceplates, mounted to the printed wiring boards, are located side by side on a shelf in the rack. To provide EMC compliance (for both emissions and susceptibility), gaps/slits between the faceplates and between the faceplate and the shelf (i.e., on the top and bottom) should be sealed. Previous attempts to seal the gaps/slits between the faceplates included the use of an EMC gasket placed on one side of each faceplate to seal against the flat surface of an adjacent faceplate. Previous attempts to seal the gaps/slits between the faceplates and the shelf included the use of a custom gasket generally placed on the top and bottom of the shelf""s frontal edges to seal against the flat surface of the faceplate.
A problem that arises with those devices and methods is that a non-continuous seal often forms between the mating faceplates and/or between the faceplates and the shelf. This creates slot antennas, which become the cause of EMC leakage. This non-continuous seal can be caused by a creased gasket, an oxidized gasket and/or oxidized base metal contacting the gasket, or an inadequate mating force. Oxidation of the gasket material and/or the base metal contacting the gasket material can also render the surface non-conductive, thereby reducing the effectiveness of the electrical contact and consequently the EMC seal. Moreover, the gasket may not have been placed on the shelf and/or faceplate following vendor specifications of surface treatment, adhesive curing time and temperature, handling, and the like, thus rendering the gasket deficient.
Efforts have been made to improve the EMC sealing between the faceplates, and between the faceplates and shelf. For instance, improvements are shown by increasing the mating force/pressure providing special surface treatment of the gasket and/or mating surface, and special handling or packaging of the gasket, faceplate, and shelf to avoid creasing, tearing and oxidation. Those solutions have either been unsuccessful or have significantly increased the cost of the devices.
Accordingly, there is a need for an EMC sealed joint that provides an effective EMC seal while minimizing or eliminating the necessity to increase the mating force/pressure, the necessity to provide special surface treatment of the gasket and/or mating surface, and/or the necessity to provide special handling or packaging of the gasket, faceplate or shelf to avoid creasing, tearing, or oxidation. In particular, there is a need for a faceplate that insures electrical contact with an effective EMC seal between the top and bottom edges of a shelf and/or between adjacent faceplates in compliance with industry standards for EMC and ESD.
In accordance with one aspect of the present invention, a faceplate is provided for electrically contacting and sealing against an adjacent faceplate in an electronic equipment rack. The faceplate comprises a front portion, a first side portion extending from one side of the front portion for receiving an EMC gasket, and a second side portion extending from an opposite side of the front portion. The second side portion has a concave groove forming edges at each side of the concave groove. The concave groove mates with an EMC gasket on the adjacent faceplate. The concave groove is preferably formed between flat surfaces on the second side portion such that the edges are formed where the concave groove meets the flat surfaces.
In accordance with another aspect of the present invention, a faceplate is provided for electrically contacting and sealing against a shelf in an electronic equipment rack. The faceplate comprises a front portion having a series of protrusions located on a back surface of the front portion at least in the regions of the back surface that contact respective edges of the shelf. At least one side portion extends from one side of the front portion, for mounting to a printed wiring board.
According to a preferred embodiment of the faceplate for sealing against the shelf, the protrusions include ribs. The ribs preferably extend the length of the front portion and are spaced at predetermined intervals, for example, to maximize the EMC seal by minimizing the size of the slot antenna intervals. Alternatively, the protrusions include dimples located at least near the ends of the front portion and spaced at intervals. The protrusions preferably have a convex outer surface.
In accordance with another aspect of the present invention, a faceplate is provided for electrically contacting and sealing against both an adjacent faceplate and a shelf in an electronic equipment rack. The faceplate includes the protrusions for contacting the shelf edges and the concave groove for receiving an EMC gasket on an adjacent faceplate.
In accordance with another aspect of the present invention, an EMC sealed joint comprises a first electromagnetically conductive member, an EMC gasket attached to the first electromagnetically conductive member, and a second electromagnetically conductive member including a concave groove with edges. The concave groove mates with the EMC gasket such that a portion of the outer convex surface of the EMC gasket sits in the concave groove. The edges of the concave groove make contact with the EMC gasket such that the interface of the EMC gasket and the second electromagnetically conductive member is overlapping in the concave/convex interface and the interference with the two edges of the groove. In a preferred embodiment, the electromagnetically conductive member may be metal or a composite, including an electromagnetically conductive layer.
In accordance with another aspect of the present invention, an EMC sealed joint comprises a first electromagnetically conductive member having a flat surface, and a second electromagnetically conductive member including a plurality of convex protrusions, such as ribs, in contact with the flat surface of the first electromagnetically conductive member. The convex protrusions are spaced at predetermined intervals on the second electromagnetically conductive member to maximize efficiency of the EMC seal. In a preferred embodiment, the electromagnetically conductive member may be metal, or a composite, including an electromagnetically conductive layer.
In accordance with a further aspect of the present invention, a mating faceplate assembly comprises at least first and second faceplates and an EMC gasket attached to the first side portion of the first faceplate such that the EMC gasket mates with the concave groove of the second faceplate.
In accordance with yet another aspect of the present invention, a rack assembly comprises first and second shelf edge portions, and at least first and second faceplates positioned against the shelf edge portions. Each of the faceplates comprises a front portion having a series of protrusions located on a back surface thereof. The protrusions are located at least in the regions of the back surface that contact the shelf edge portions. At least first and second printed wiring boards are mounted to the respective faceplates.